Abstract: Mass scaling factor is one of important parameters in an explicit finite element analysis. Effect of the mass scaling factor on the temperature field of the plunge stage in friction stir welding (FSW) was studied, and the optimization of 3D explicit finite element analysis of FSW was obtained. Results show that the mass scaling factor has a significant influence on the computation time and the displacement of the tool. A reasonable temperature field can be obtained with less computation time when the mass scaling factor is 10⁶. Furthermore, the simulated temperature data corresponds well with the experimental data from the literature.